6021980-UIM-A-1120
Johnson Controls Ducted Systems
71
Smart Equipment™ UCB - limit, 24 VAC power, and shutdown connections
Location
Label
Description
Function and comments
B
LIMIT
Monitored 24 VAC input through heat section
limit switch(es)
If voltage is absent, indicating the heat section is over-temperature, the UCB will
bring on the indoor blower
C
24 VAC, 75 VA transformer Common
referenced to cabinet ground
Connects through circuit traces to thermostat connection strip C and indoor
blower VFD pin C
24V
24 VAC, 75 VA transformer hot
Powers the UCB microprocessor, connects through circuit trace to the SD 24
terminal
SD 24
24 VAC hot out for factory accessory smoke
detector, condensate overflow and/or user
shutdown relay switching in series
Connects through circuit trace to thermostat connection strip SD-24. A wiring
harness jumper plug connecting SD 24 to SD R is in place if factory accessories
for unit shutdown are not used - this jumper plug must be removed if the
switching of field-added external accessories for unit shutdown are wired
between thermostat connection strip SD-24 and R
SD R
24 VAC hot return from factory accessory
smoke detector, condensate overflow and
user shutdown relay switching in series
Connects through circuit trace to the R terminal on the upper left of the board
R
24 VAC hot for switched inputs to the UCB
Connects through circuit trace to the thermostat connection strip R terminal,
right FAN OVR pin, right HPS1 pin, right HPS2 pin, lower DFS pin and lower
APS pin
Smart Equipment™ UCB - space temperature sensor connections
Location
Label
Description
Function and comments
C
ST
Space Temperature sensor input from 10K
Ω
@
77°F, Type III negative temperature coefficient
thermistor
Positive of VDC circuit (3.625 VDC reading to COM with open circuit),
effective if “Thermo- stat-only Control” parameter is set OFF, space
sensor override momentary shorts ST to COM to initiate/terminate
temporary occupancy
COM
Common for ST and SSO inputs
Negative of VDC circuit for ST and SSO inputs
SSO
Space Sensor Offset input from 0 to 20K
Ω
potentiometer
Positive of VDC circuit (3.625 VDC reading to COM with open circuit),
10K
Ω
/2.5 VDC is 0°F offset, 0
Ω
/0 VDC is maximum above offset and
20K
Ω
/3.4 VDC is maximum below offset from active space temperature
setpoint
Smart Equipment™ UCB - temperature sensor connections
Location
Label
Description
Function and comments
D
SAT+
Supply Air Temperature sensor input from 10K
Ω
@ 77
°
F, Type III negative temperature coefficient
thermistor
Input required for operation; 3.625 VDC reading SAT+ to SAT
–
with open
circuit. Used in heat/cool staging cutouts, free cooling operation, demand
ventilation operation, comfort ventilation operation, economizer loading
operation, VAV cooling operation, hydronic heat operation.
RAT+
Return Air Temperature sensor input from 10K
Ω
@ 77°F, Type III negative temperature coefficient
thermistor
Input required for operation; 3.625 VDC reading RAT+ to RAT
–
with open
circuit. Used in return air enthalpy calculation. Substitutes for space
temperature if no other space temperature input is present.
OAT+
Outside Air Temperature sensor input from 10K
Ω
@ 77°F, Type III negative temperature coefficient
thermistor
Input required for operation but may be a communicated value; 3.625 VDC
reading OAT+ to OAT
–
with open circuit. Used in heat/cool cutouts, low
ambient cooling determination, dry bulb free cooling changeover, outside
air enthalpy calculation, economizer loading operation, heat pump demand
defrost calculation.
CC1+
#1 refrigerant circuit Condenser Coil temperature
sensor input from 10K
Ω
@ 77°F, Type III negative
temperature coefficient thermistor
Input required for heat pump units, not required for A/C units; 3.625 VDC
reading CC1+ to CC1
–
with open circuit. Used in heat pump demand
defrost calculation.
EC1+
#1 refrigerant circuit Evaporator Coil temperature
sensor input from 10K
Ω
@ 77°F, Type III negative
temperature coefficient thermistor
Input required for operation; 3.625 VDC reading EC1+ to EC1
–
with open
circuit. Used in suction line temperature safety.
